Acorn's RiscPC can emulate a PC using a small plug-in card, of which several types have been available over the years. These cards plug into the second processor slot in an Acorn or Castle RiscPC and share the computer's resources such as keyboard, mouse, display and disk drives, thanks to a clever chip called Gemini.
Because the disk formatting is different from the native RISC OS format, the PC files are kept in a pseudo drive—actually a file containing files. This is a so-called partition file, and is typically called Drive_C. A second partition can be set up (Drive_D), and these can be any suitable size up to 2 GBytes apiece. The driving software allows for a number of different configurations, each of which can (but doesn't have to) have different partitions. For example, some users have separate Drive_C partitions for running DOS and Windows (typically 95 or 98, but sometimes Win 3·11).
There are a number of advantages to this arrangement:
This is the base-model 486-processor PC Card. Others were available from Acorn and other sources such as Aleph One, up to a 133 MHz 586-processor card.
This photograph shows the PC/Second Processor Card installed in its slot in an Acorn RiscPC. Here are some screenshots showing what the PC Card can do.
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